Aerospace vehicles, including aircraft and spacecraft, often operate at altitudes where the air is inhospitable to humans. Accordingly, such vehicles are hermetically sealed and pressurized, and Environmental Control Systems (ECS) that manage interior air quality have long been a part of aerospace vehicle design. For example, U.S. Pat. No. 7,871,038, “Systems and Methods for Providing Airflow in an Aerospace Vehicle,” issued Jan. 18, 2011 to the assignee of the present application describes, in the context of a passenger airplane, automated systems and methods to blend external air from an outside air supply with recirculated air. The '038 patent also describes controlling air quality parameters, such as the recirculation flow rate, based on factors such as contaminant level and temperature. Aspects of the present disclosure are similarly described herein in the context of a passenger airplane, although this is only to provide a context for description, and does not limit the scope of the disclosure.
A conventional approach to maintaining interior air quality has been to filter the interior air as part of a recirculation process, and also to “refresh” the air by mixing it with outside air. In order to increase the efficiency, range, & flexibility of the airplane, a more efficient method of providing airflow and maintaining equipment is desired to optimize airflow to what is required by the airplane and its passengers, while maintaining occupant comfort.
Standard sea level (SSL) air is 59° F. and at a pressure of 14.7 psi. At 35,000 feet, the air is −66° F. and 3.5 psi. Because of the very low temperature, outside air at high altitude contains very little moisture. Accordingly, to condition outside air for consumption in an airplane, it must be pressurized, heated, and humidified. All of these modifications require energy, and hence consume fuel. Additionally, air at high altitude contains significant levels of ozone (O3).
It is known to deploy either an ozone converter or a combination Volatile Organic Compound (VOC) and ozone converter in passenger aircraft. The ozone and VOC/ozone converters can increase the aircraft maintenance load, as the converters must be periodically cleaned and eventually replaced. To extend converter life, it is typical to control the interior air to bypass ozone or VOC/ozone converters when contaminants exist which are bad for converters but not necessarily for people. For example, on the ground in an airport environment, there can be an elevated concentration of sulfur dioxide. This can have significant effects on the lifespan of an ozone converter.
The Background section of this document is provided to place examples of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.